by the hour

by the hour

1. Per hour; at an hourly rate. Of course he's drawing out this project—he gets paid by the hour!
2. Every hour; once an hour. I feel better knowing that the nurse will check on mom by the hour. Sir, the situation is worsening by the hour—how should we proceed?
See also: by, hour
Farlex Dictionary of Idioms.

by the hour

at each hour; once each hour. It kept growing darker by the hour. I have to take this medicine by the hour.
See also: by, hour
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs.
See also:
  • till all hours
  • till all hours (of the day and night)
  • till/until all hours
  • on the hour
  • on the hour/half-hour
  • the top of the hour
  • be on the hour
  • zero hour
  • at the top of the hour
  • in (one's) hour of need
References in classic literature
She would sit and smooth his forehead by the hour, and talk to him and try to make him forget.
Teta Elzbieta would put the clothesbasket in which the baby slept alongside of his mattress, and Jurgis would lie upon one elbow and watch him by the hour, imagining things.
Fogg, played whist by the hour together in absorbing silence.
Even if they don't publicly object to the deal you've cut, they're going to go nuts when they figure out that you're getting paid by the hour. (This is the most common arrangement and includes pro-rated benefits.) That means you don't have to put in unpaid overtime, which is, of course, one of the powerful attractions of part-time work.
* Accounting for use of personal or sick leave time by the hour.
But because most drivers are paid by the mile rather than by the hour, expenses wouldn't be affected.